Paraprotein in the blood: is it a sign of cancer?

Some people make an abnormal amount of protein called a paraprotein or 'M protein' that can be found in their urine or blood. There are different conditions that can cause a paraprotein, with the most common being monoclonal gammopathy of unknown significance (MGUS). In most cases, this is a non-cancerous condition but another, more serious, blood abnormality linked to a paraprotein is myeloma.

One of our top haematologists Dr Jonathan Sive explains how a paraprotein is detected, what the possible causes are and what happens following diagnosis.

What is a paraprotein?

A paraprotein is an abnormal protein that is produced by plasma cells in the bone marrow. Plasma cells are specialised blood cells that usually produce a range of different proteins called immunoglobulins as part of the body’s immune system. If a group of plasma cell starts to produce just one type of abnormal protein this is called a paraprotein and can be an indicator of an abnormality. It may also be referred to as an “M-band” or “M-protein”.
 

How is it detected?

A paraprotein can be detected in the blood using tests called Serum Protein Electrophoresis and Serum Free Light Chains. These will detect slightly different kinds of paraproteins (“Intact Paraprotein” or “Light Chain”), but they are both produced by the same process and are usually managed the same way. When a paraprotein is detected in the urine it is sometimes referred to as “Bence-Jones protein”.
 

What causes a paraprotein?

There are a number of different conditions that can cause a paraprotein. Commonly, they are produced by a condition called MGUS. This is a benign condition. Although it can occasionally turn into more serious conditions, this happens rarely and MGUS can usually be safely monitored.

Occasionally, paraproteins may be a sign of a serious blood abnormality called myeloma. This is usually accompanied by signs of damage to the body such as fatigue from low red blood cells (anaemia), kidney problems, high calcium or bone damage.

More rarely, paraproteins can be caused by other blood conditions such as lymphomas, and sometimes they can occur with infections, liver problems or inflammatory conditions.
 

Read more: on treatment for myeloma

What should I do if a paraprotein is detected?

Your doctor may refer you to a haematologist (blood specialist) for further tests, which may include blood and urine tests, scans and sometimes a bone marrow biopsy test. If a serious abnormality such as myeloma is detected, they may recommend starting some treatment. If it found to be MGUS or another benign condition, then this could be safely monitored either by the specialist or your GP.

Book an appointment with Dr Sive today.